Radiation-sensitive compositions are routinely used in the preparation of imageable materials including lithographic printing plate precursors. Such compositions generally include a radiation-sensitive component, an initiator system, and a binder, each of which has been the focus of research to provide various improvements in physical properties and thereby imaging performance.
Recent developments in the field of printing plate precursors concern the use of radiation-sensitive compositions that can be imaged by means of lasers or laser diodes, and more particularly, that can be imaged and/or developed on-press. Laser exposure does not require conventional silver halide graphic arts films as intermediate information carriers (or “masks”) since the lasers can be controlled directly by computers. High-performance lasers or laser-diodes that are used in commercially-available image-setters generally emit radiation having a wavelength of at least 700 nm, and thus the radiation-sensitive compositions are required to be sensitive in the near-infrared or infrared region of the electromagnetic spectrum. However, other useful radiation-sensitive compositions are designed for imaging with ultraviolet or visible radiation.
There are two possible ways of using radiation-sensitive compositions for the preparation of printing plates. For negative-working printing plates, exposed regions in the radiation-sensitive compositions are hardened and unexposed regions are washed off during development. For positive-working printing plates, the exposed regions are dissolved in a developer and the unexposed regions become an image.
Negative-working radiation-sensitive compositions and imageable elements are described for example, in U.S. Pat. No. 6,309,792 (Hauck et al.), U.S. Pat. No. 6,569,603 (Furukawa et al.), and U.S. Pat. No. 6,899,994 (Huang et al.), and EP 1,182,033 (Fujimako et al.) and EP 1,449,650 (Goto).
Problem to be Solved
U.S. Pat. No. 4,774,163 (Higashi) describes photopolymerizable compositions containing a carbazole derivative and optionally a linear polymer binder for photoresists and printing plate preparation.
While many known negative-working radiation sensitive compositions have found usefulness in the industry, there continues to be a need to improve photosensitivity. In addition, known negative-working imageable elements often require a pre-heat step after imagewise exposure and before development in order to enhance the crosslinking within the imageable layer.
There is a desire in the industry to reduce processing steps where possible including the conventional pre-heat step. There is also a need to have compositions of this type that can be imaged using a variety of imaging devices at various wavelengths from 150 to 1500 nm.